1. Field of the Invention
The present invention relates to a teaching method and teaching means for bonding coordinates, particularly to bonding coordinates of leads of lead frames connected to semiconductor chips.
2. Prior Art
As seen from FIG. 6, a workpiece 3 is obtained by connecting the pads P.sub.1, P.sub.2 . . . ) of a semiconductor chip 2 and the leads L.sub.1, L.sub.2 . . . ) of a lead frame 1 via wires 4, and such connections are performed by a wire bonding apparatus shown as an example in FIG. 7.
In the wire bonding method that is exercised by the bonding apparatus shown in FIG. 7, any positional discrepancy is first detected at at least two fixed points on the semiconductor chip 2 and at least two fixed points on the lead frame 1 by a camera 11, and bonding coordinates stored beforehand are corrected via the operating part of the bonding apparatus on the basis of these detected values.
When the detection by the camera 11 is performed, an X-axis motor 12 and a Y-axis motor 13 are actuated so that the central (optical) axis 11a of the camera 11 is positioned directly above each measurement point. After the bonding coordinates have been corrected, a capillary 15 is moved in X and Y directions, or horizontally, and in the Z direction, or vertically, so that a wire 4 passing through the capillary 15 is bonded to the workpiece.
In this bonding method, the central axis 11a of the camera 11 and the central axis 15a of the capillary 15 are offset by a distance W. Accordingly, an XY table 16 is moved a distance equal to the an offset value W by the X- and Y-axis motors 12 and 13, so that the capillary 15 is positioned above the first bonding point. Afterward, the wire 4 is bonded at the corrected bonding coordinates by moving the XY table in XY directions by the X- and Y-axis motors 12 and 13 and also by moving the capillary 15 in the Z direction by raising and lowering a capillary arm 17 (or pivoting the capillary arm 17) by a Z-axis motor 14.
In FIG. 7, Xw indicates the X-axis component of the offset value W, and Yw indicates the Y-axis component of the offset value W.
In the wire bonding method as described above, it is necessary to input respective bonding coordinates into the memory of the bonding apparatus before the wire bonding operation. Such input of bonding coordinates is also necessary when the type of workpiece to be wire-bonded is changed. These respective bonding coordinates to be inputted include the bonding coordinates of pads P.sub.1, P.sub.2 . . . and the bonding coordinates of corresponding leads L.sub.1, L.sub.2 . . . , and the inputting of these respective bonding coordinates into the bonding apparatus is generally accomplished by means of a teaching method.
Conventionally, the teaching of the respective bonding coordinates of the leads L.sub.1, L.sub.2 . . . is accomplished in the following manner:
a. First, a manual input device such as a ten-key, chessman, etc., which drives the X-axis motor 12 and Y-axis motor 13 is manually operated so that the coordinates L.sub.1 (x.sub.1, y.sub.2) of the first lead L.sub.1 are inputted. These coordinates are shown on a television monitor.
b. Next, the operator, while watching the monitor, operates the manual input device so that the position that appears to be the bonding coordinates of the first lead L.sub.1 is aligned with cross-hairs drawn at the center of the television monitor. This coordinate position is stored in the memory of the bonding apparatus.
The operation described above is performed for all of the leads L.sub.1, L.sub.2 . . . . The teaching of the bonding coordinates for the pads P.sub.1, P.sub.2 . . . of a semiconductor chip is accomplished in a similar manner.
In the prior art described above, the operator teaches bonding coordinates by operating the manual input device in a specified order. Thus, the positional alignment operation must be repeated a number of times equal to the number of sets of bonding coordinates involved. As a result, it takes considerable time. In addition, chances are that alignment errors occur as a result of mistakes made by the operator and differences between individual operators. Furthermore, in such a manual input, the clearness of the object images on the monitor is determined by the resolution of the monitor. As a result, finer positions than the monitor is capable of showing cannot be seen nor judged, and the positional precision is determined on the basis of pixel (picture element) units.